Vibrational transitions in excited states of molecules using coherent stokes raman spectroscopy: application to ferrocytochrome-C

Abstract

We introduce a new technique for the study of excited state spectra. The method relies on the fully resonant coherent Stokes light generation which is shown to display peaks at excited state vibrational intervals even though there is initially no population in these levels. The spectra that can be obtained of the excited states are free from electronic dephasing and can be used to clarify contested spectra of molecules in all media. The archtypical broad-banded spectrum of ferrocytochrome-c showing no structure in its Soret region is used to demonstrate possibilities for this new method. The oxidation marker vibrational band at 1362 cm −1 of the ground state is suggested to occur in the electronically excited Soret state at 1339.5 cm −1. The presumed excited state vibrational transition has a width of 8.5 cm −1 (1 / T 2) which is used to place limits on the population relaxation time of this state. Results are also presented for the coherent anti-Stokes signals of both ferri- and ferrocytochrome-c.